According to the blogpost, PDF rendering will be contained within the security sandbox Chrome uses for web page rendering. Users will automatically receive the latest version of Chrome’s PDF support; they won’t have to worry about manually updating any plug-ins or programs.

The plug-in can be enabled by going to chrome://plugins/ and clicking on "Enable" for the "Chrome PDF Viewer" plug-in. While you are at it, I would recommend you disable any other PDF plugins.